1. Field of the Invention
This invention relates to the field of positioning the head assemblies of disk storage mechanisms, particularly during seek operations.
2. Background Art
In present day data processing systems, it is desired to provide a large amount of memory which can be accessed in a minimum amount of time. One type of memory which has enjoyed widespread use in the data processing field is that of magnetic media disk memories.
In general, disk memories are characterized by the use of one or more magnetic media disks stacked on a spindle assembly and rotating at a high rate of speed. Each disk is divided into a plurality of concentric "tracks" with each track being an addressable area of the memory array. The individual tracks are accessed through magnetic "heads" which fly over the disks on a thin layer of air. Typically, the disks are two sided with a head accessing each side.
The heads are in substantial alignment and are pivotally mounted to an actuator motor. The actuator motor may be a "voice coil" electrodynamic motor which has a coil moving within a permanent magnet, defining a cylindrical core. Alternatively, the motor may have a "rotary" type coil, such as is described in U.S. patent application Ser. No. 444,465 filed on Nov. 24, 1982, and U.S. patent application Ser. No. 893,955 filed on Aug. 7, 1986, both assigned to the assignee of the present invention. The motor is used to swing the heads back and forth over the disks so as to access various of the tracks. The maximum acceleration and velocity of the heads across the disk is dependent upon the strength of the magnets used in the voice coil assembly and the amount of current transmitted to the coil.
The various tracks are identified through servo information located within each track or stored on a dedicated servo disk. The position of each of the heads is fixed relative to every other head so that by positioning a servo head over a particular track on a servo disk, each of the other heads will be located in a repeatable position.
The process of moving a head from a current position to a desired position is known as a "seek". To maximize the performance of a disk drive memory, it is desired to minimize the seek time. In the prior art, one method of minimizing seek time is to instantly bring the heads to a maximum acceleration so that there will be a linear increase in velocity up to a maximum or peak velocity. Approximately half way through the seek cycle, the heads are subjected to maximum deceleration resulting in a linear decrease in velocity until the heads come to a stop over the desired track.
One disadvantage associated with this method of performing seeks is the large amount of acoustical noise which accompanies the seek operation. To minimize acoustical noise, the prior art has either utilized acoustic damping material around the disk drive assembly, which has the disadvantage of adding to the weight, cost and size of the disk drive assembly, or it has slowed down current rise times by increasing the L/R time constant of the voice coil. This has the disadvantage of causing additional phase lag in the position loop which makes stablizing the loop more difficult.
Therefore, it is an object of the present invention to provide a method and apparatus for performing seeks which results in a reduction in accoustical noise, without additional phase lag.
It is a further object of the present invention to provide a method and apparatus of performing seeks which does not add to the time required for performing the seek.
It is yet another object of the present invention to provide a method and apparatus for performing seeks which can be adapted for use in a variety of disk drive systems.
It is a still further object of the present invention to provide a method and apparatus for performing seeks which can be utilized to perform other tasks in the disk drive system.